High pressure water jet cutting is accomplished using water pressures of several thousand psi. In a typical water jet cutting system, tap water is pressurized in a double-acting pumping system, stored in a high pressure accumulator wherein the compressed water pressure is stabilized, and withdrawn from the intensifier system through a water jet nozzle. Between the intensifier and the jet nozzle, a valve is usually required to open and close the flow of pressurized water to the jet nozzle. Without such a valve, the entire intensifier system must be shut down to stop water outflow; a major inconvenience.
Among the on-off valve designs proposed by the prior art, a common design has incorporated a hydraulic or pneumatic circuit into the water jet nozzle on-off valve which closes the valve by application of pressurized fluid and opens the valve by release of hydraulic fluid pressure from the valve, allowing the pressurized water itself to force the valve stem open. This design is a simple and straight forward solution but poses safety problems. If, in such a design, fluid pressure is lost when it is intended that the valve remain closed, the sudden opening of the valve as a result of lost hydraulic fluid pressure could be dangerous. Likewise, if the valve is closed and then the system is turned off, even though intentionally, because hydraulic fluid pressure will decay more rapidly than that of the hight pressure water system, at some intermediate pressure the valve will open unexpectedly; again posing a possible hazzard to an operator.
Because of the above delineated problems, it has been posed that hydraulic or pneumatic fluid under pressure ought to be instead directed to open the on-off valve, rather than close it. In such a design, some external force must be applied to close the valve after venting the hydraulic fluid. In such a design, the external force must be sufficiently large to overcome the opening force exerted by the high pressure water present in the valve which works against the valve stem. The solutions to this have included the use of large, bulky Belleville springs, resulting in cumbersome and heavy valve mechanisms.